Xerographic wet belt loading



June 3, 1958 c, KAlsER 2,837,441

XEROGRAPHIC WET BELT LOADING Filed Feb. 1, 1955 POWDER PARTICLES INLIQUID SUSPENSION INVEN TOR. CARL B. KAISER F MW ATTORNEY United StatesPatent XEROGRAPHIC WET BELT LOADING Carl E. Kaiser, Rochester, N. Y.,assignor to The Halolil Company, Rochester, N. Y., a corporation NewYork Application February 1, 1955, Serial No. 435,548

3 Claims. (Cl. Ill-47.5)

This invention relates in general to Xerography and in particular todevelopment of electrostatic charge patterns.

ferography uses the physical phenomenaof photoconductivity andelectrostatic attraction of electrostatically charged bodies to converta light image into a physical image consisting of, for instance, blackpowder on white paper. The xerographic plate may consist of a film of aphotoconductive insulating material on a conductive backing member. inuse, the plate is generally given an electrostatic surface charge andthen exposed to a light image, which results in an electrostatic imageon the plate surface. This electrostatic image, which may be allowed toremain on the plate or which may be transferred, is developed byallowing it to attract and collect electrically charged particles ofpowder. The powder image may then be transferred and fixed to anothersurface, usually a sheet of paper, and the plate may be cleaned forreuse, or the powder image may be allowed to remain on the plate forphotographing, viewing or the like.

Different methods of image development are in use. One form ofdevelopment is known as powder cloud development and is described, forexample, in Carlson U. S. Patent 2,221,776. In this technique fordevelopment, a dispersion of powder particlesvin gas is passed to thesurface area bearing the electrical image and properly charged particlesare drawn out of the cloud to form a powder deposition in electricalimage configuration.

An object in the art of Xerography, as in any art concerned with imagereproduction, is that of uniformly developing high quality copy. Meansof obtaining this objective while using powder cloud development, isthrough the uniform and constant presentation to the electrostaticcharge pattern on a surface of a powder cloud of fine developer powderparticles uniformly and densely dispersed throughout.

Powder clouds of dense and uniform dispersion of powder particles may begenerated by passing a tape or belt of cloth or the like which has beenuniformly loaded with powder articles over an output tube at a uniformrate. Particles are blown from the belt or tape in a controlled gasstream thereby producing a controlled aerosol of uniformly constant anddense dispersion of powder particles. This invention is concerned withthe uniform loading of belts, ribbons, tapes and the like with powderedparticles.

Thus, it is an object of this invention to devise new means and methodsfor impregnating or loading tapes, belts, ribbons or the like materialwith Xerographic developer powder particles.

A method which has been used heretofore in the art of Xerography toimpregnate or load tapes, belts, ribbons or the like with powderparticles has involved conveying an aerosol of powder particles to aloading zone through which a tape, ribbon, belt or like material movesat a uniform rate of speed. The aerosol is blown to and through the tapeor the like, and particles tend to load in the material, therebycreating impregnated or loaded 2I,S3?,44l Patented June 3, 1 958 tapesof material. This invention accomplishes loading by immersion of a tape,ribbon, belt or like material into a liquid dispersion of Xerograplncdeveloper powder particles. The belt is thenremoved from the dispersionand allowed to dry and is then ready for use in powder cloud beltgenerators.

The term dispersion is used herein in both the specification and claimsto include monomolecular dispersions, i. e. solutions, andmacromolecular dispersions. i. e. suspensions of developer particles ina suitable liquid.

It is, therefore, an object of this invention to devise new means andmethods for impregnating through immersion tapes, ribbons, belts or likematerial with xerographic developer powder particles.

For a better understanding of this invention, together with otherfurther objects thereof, reference is now had to the followingdescription taken in connection with the accompanying drawings, and thescope of the invention will be pointed out in the appended claims.

Fig. l is an isometric view of an embodiment of a belt, ribbon, tape orlike material stretched between two spools.

Fig. 2 is a cutaway isometric view of one possible embodiment of thisinvention showing immersion of a belt, tape, ribbon or like materialimmersed in a dispersion having Xerographic developer powder particlesdispersed throughout a liquid.

For a more thorough discussion of this invention, reference is now hadto Fig. 1 wherein is shown in detail an embodiment of a belt, ribbon,tape or like material according to this invention. As appears in thisfigure, a belt 11 of material stretches between spool 12 and spool 13.It is to be realized that the object of this invention is that ofloading belts, tapes, ribbons, and the like of material, and there is nointent to limit this invention to belts stretched between spools asshown in this particular figure. When a tape of material or the like hasbeen impre nated or loaded with developer powder particles, it may thenbe wound on spools to produce a belt similar to the one shown in Fig. 1,or it may be kept in other ways for later use. An impregnated belt onspools as shown in this figure may be used directly in belt powder cloudgenerator devices simply by inserting the spools in their proper placesin the apparatus and operating the equipment. During operation, the beltwill move at a uniform rate over an output tube and a constant, steadyflow of gas will cause removal of the particles in the belt into a gasstream, thereby creating an aerosol of powder particles. The aerosol maythen be conveyed to the development zone for deposition of the powderparticles on an electric charge pattern bearing surface. Beforedeposition, the particles in the aerosol may be charged ordeagglomerated, or both, in order to bring about fine grain Xerographicdevelopment.

Reference is now had to Fig. 2 wherein is shown a tray 15 holding adispersion of xerographic developer powder particles in a liquid 16. Atape, band, ribbon or belt of material 17 is positioned beneath thesurface of the liquid dispersion 16 and therein becomes impregnated,coated or loaded with xerographic developer powder particles.

The liquid dispersion is composed of a liquid in which is dispersedxerographic developer powder particles. The liquid may be any liquid,and is preferably a liquid which will not dissolve and will suspend thexerographic developer powder particles in the dispersion. Although asolvent for the particles will act to bring about a uniform dispersion,the particles when loaded will to some extent be fused to one anotherand many agglomerates of particles will be present. A non-solventsuspending agent, on the other hand, will produce a loaded belt composedof individual and deagg'lomerated particles. Such non-solvent liquidsinclude, but are in no way limited to, fluoro-chloroalkanes availableunder the general family name of Freon, water, dioxane,trichloroethylene, trichloroethane, dichloroethylene, dichloroethane,and the like. It is to be realized that some of these liquids will actas a solvent for some powders, but not for all, and whether or not theliquid acts as a solvent is, of course, dependent on what the developeris composed of. For example, different types of carbon particles areused in some applications of the art of xerography, and no solventexists for some of these materials. in such an instance, any liquidwhich will not affect the belt material detrimentally may be used.

Desirably also, the liquid is a volatile substance. Ecfore being used inpowder cloud generators, the impregnated or loaded tape or belt ofmaterial must be dried. Drying takes place with greater rapidity whenthe tape or belt of material has been immersed for loading purposes in aliquid dispersion in which the liquid is volatile. Although it is notintended to limit this inventon in any way to the following, they arelisted as examples of usable volatile liquids. They are isopropylalcohol, heptane,

sulfur dioxide, acetone, ethanol, methanol, and the like.

Xerographic developer powder particles comprise varying materials, andsatisfactory prints or pictures may be produced with belts or tapesloaded or impregnated with the various developer materials. For example,any of a number of various carbon or lamp black materials may beemployed, including such materials as furnace blacks, channel blacks,and the like. In addition, there may be used such materials as milledcharcoals and similar materials, or, if desired, finely dividedmaterials having added pigment matter. in the latter category arematerials such as finely divided resins containing pigments or dyes suchas carbonaceous pigments or various coloring pigments, and the like,compositions of this type being preferred where the final print orpicture utimately is to be made permanent by a fusing process includingheat or vapor fusing. For highest quality continuous tone xerographicWork, the presently preferred material is charcoal. Any

and all of these materials which have been found to work well inproducing good quality xerographic prints may be used as the xerographicdeveloper powder particles to be held in liquid dispersion to load,through immersion, belts, tapes or like material.

Although in Fig. 2 the tape 17 is shown suspended horizontally in a flattray within the liquid dispersion held by the tray, it is to be realizedthat other techniques of immersion and loading may be used and areintended to be encompassed by this invention. The liquid dispersion, forexample, may be encased in a container such as a tube or graduate andthe tape or belt may be allowed to hang from the top downward into theliquid dispersion, or, using a tray as shown in Fig. 2, the belt or tapeof material may be continuously moved through the liquid dispersion, asfor example, a roll of photographic film is moved during traydevelopment. It is also possible to impregnate or load tapes or belts ofmaterial by simply dipping the belt or tape of material into and out ofa proper liquid dispersion.

It has been found through experimentation that leeway exists in thiscoating operation and that the function of the dipping operation is thatof loading or impregnating the tape or belt of material with powderparticles. Uniformity in load is desired and uniformity may be obtainedby allowing the liquid dispersion to contact all areas of the beltthrough a uniform time period. The time period may be very brief, as forexample, dipping in and out, or the time period may extend over manyminutes or a longer period than that. The load to the belt followingimmersion or dipping will depend on such factors as the density ofzerographic developer powder particles in the liquid dispersion, theability of the tape 0r belt of material to load with xerographicdeveloper powder particles through immersion, the time the belt or tapeof material is in the liquid dispersion, and the like.

An important consideration in forming belts for high quality xerographicreproduction is the belt material itself. The material should be uniformthroughout. This will assure presentation to the liquid dispersion ofpowder particles of a material which is at all points able to hold andaccept the same amount of particles one which will tend to impregnatewith an equal amount of particles throughout when immersed in auniformly dispersed solution or suspension of powder particles inliquid. The belt material should also be a porous ma terial, which willallow the gas of the belt powder cloud generator to pass through it whenthe aerosol of powder particles is being created. Any material capableof accepting and holding powder particles when immersed in a liquiddispersion of powder particles is intended to be encompassed within thescope of this invention. To date, the best materials have been foundgenerally to napped cloth materials, as for example, velvet, velveteen,woolens, terry cloth, napped rayon and the ill: Napped cotton flanneland equivalent materials are the preferred materials as belt materialfor loading purposes through immersion. An equivalent material forcotton flannel would be cotton tape or bias material with a mappedsurface or napped surfaces. The preferred materials have been foundgenerally to accept a more uniform and denser load or impregnation thanother materials lacking the napped surfaces. It is to be realized, also,that other materials such as 2. treated mesh metal screen will alsowork, and such other materials whether pretreated or not, which willload when immersed, are intended to be encompassed herein.

The loaded or impregnated belt or tape is presently believed to havepowder particles extending through all areas of thickness of the belt ortape material. The load accepted by each belt is largely dependent onthe density of the cloth and the ability of the cloth to load withpowder particles. By ability of the cloth to load, it is intended toinclude such elements as the effect of the cloths mesh and the clothsnap, and the word density is intended to include such elements as thethickness of the cloth. Powder impregnated or loaded to the belt or tapedeposits both between the threads and on the threads and between areasof napped material and on the napped material.

Belt materials, it is presently believed, have a saturation point abovewhich they tend not to accept within themselves any more xerographicdeveloper powder particles. Although powder particles may occasionallyremain resting on the surface, if they are above the saturation point,they are easily removed by simply shaking the loaded belt. Thus,particles above saturation will shake loose, whereas particles below thesaturation point will have become part of the belt material and willremain adhering to the belt material.

Experiments have been carried out loading belts using a one inch widebelt composed of white, heavy cotton flannel, four ounces per yard, andimmersing this belt in a liquid dispersion of varying amounts of liquidand varying liquids and varying amounts of xerographic developer powderparticles and varying xerographic developer powder particles. Bestloading results have been attained as measured by the end printsproduced from the loaded belt using charcoal powder particles as thexerographic developer powder particles. Belts have been immersed forvarying times and the following specific example is only included hereinfor illustrative purposes. It is to be realized that varying times maybe used, depending upon the liquid dispersion being used, belt materialbeing used, and the like, and equal results may be obtained. In thisparticular instance a suspension composed of three parts charcoal tosixteen parts water was used, and the belt or tape of material-wasim-rmersed in this suspension for six minutes and resulted in a highlyuniform and dense load or impregnation of powder particles in the cottonflannel napped cloth. The load accepted by the belt was found to be 528mgms. per foot. Using a similar suspension made up of four partscharcoal to sixteen parts water, it has been found that the tapes ondrying tend to have caked particles on the surface of the tape material.These particles may be removed by brushing the surface lightly or byshaking the material. However, it is presently believed that it isdesirable to avoid formation of caked particles on the surface in thatless agglomerates appear in the print produced when a belt without cakedparticles is used. Using the suspension made of three parts charcoal tosixteen parts water, no caking was noticed. Less dense suspensions, suchas one part charcoal to sixteen parts water, require a longer loadingtime or result in less of a load to the belt material. Neither of theseelements is undesirable,.but are stated here to fully and clearlydisclose the methods of carrying out this invention. Experiments havealso been conducted using isopropyl alcohol as the liquid in which thesuspension is formed. In such an instance, a suspension of ten partscharcoal to sixteen parts isopropyl alcohol was found to produce highlydense and uniform loads of powder particles in the belt materials. Onthe other hand, using a solution composed of twelve parts charcoal tosixteen parts isopropyl alcohol resulted in caking on the tape material,requiring shaking or brushing off of the caked particles before the beltcould be used without producing too many agglomerates in the developedprints. Using suspensions of isopropyl alcohol having lesser amounts ofcharcoal particles produces less dense loads of charcoal particles onthe belt material, or requires more immersion time than six minutes.

After immersion of the belt in the liquid dispersion, it is necessary tocompletely dry the belt material and the xerographic developer powderparticles before using the loaded or impregnated belt in a belt powdercloud generator. This may be accomplished by hanging the belt loadedwith powder particles in a room and allowing it to dry, or it may beaccomplished by playing a heated blast of air on the belt material. Suchprocedures have been found to result in varying drying times dependingon the liquid for the dispersions, the developer, the belt material, andthe like. For example, when a belt which has been immersed in adispersion of particles in water for six minutes was hung to dry in thepath of a hot air blast, it was found to take from an hour and a half tofour hours for complete drying. When a hot air blast was not used, ithas taken as long as twelve hours to dry such a belt. When using avolatile liquid to form the dispersion, it has taken from as little asfifteen minutes to a few hours. air blast had been directed at a beltwhich had been soaked in isopropyl alcohol for six minutes, it was foundto take thirty-one minutes to dry the belt.

A technique which has been found to dry the belts faster withoutresulting in any detrimental effects to the powder particles loaded tothe belt material which will subsequently be produced into an aerosol ofpowder particles for development of xerographic electrostatic images,involves first, blotting the belt carrying particles after it is removedfrom the liquid dispersion, and then hanging the belt for dryingpurposes. Specifically, the belt loaded with powder particles may beplaced between two blotters and then passed through a conventional setof wringers as is found, for example, on ordinary wringertype washingmachines. Sufficient pressure was applied to wring out excess liquidfrom the belt material and the drying time was found to be cutsubstantially. For example, when a belt had been soaked in a waterdispersion for six minutesand then positioned in an area of hot airflow, it was found to take some twenty-three minutes to When a hot drythe belt when blotting took place. Likewise, a belt that had-beenpositioned in isopropyl alcohol for siX minutes was found to take somenine minutes to dry after being blotted.

It is presently believed that open contact of the liquid suspension withall areas of the belt is desirable to accomplish uniform and quickloading. This may be accomplished by keeping the belt in an open orunrolled or stretched-out position while immersed in the liquidsuspension.

Depending on the particular xerographic developer powder particles beingused, it is sometimes desirable to create the liquid dispersion andallow large particles or agglomerates to settle before inserting a beltfor loading purposes. In this way, loading of large particles andagglomerates of powder particles is avoided to a large extent. it isalso sometimes desirable to add to the liquid dispersion a materialwhich will aid in keeping the xerographic developer powder particlesthoroughly pended, such as for example, cellulose gum, gum tragecanth,gum arabic, or the like.

Belts described according to this invention, when used in powder cloudgenerators, have the advantage of consistency and uniformity betweenbelts with similar char acteristics. Two belts of similar materialloaded through immersion in a similar liquid dispersion for the sameamount of time will produce highly consistent and uniform cloud outputswhen used in similar powder cloud generators. Also it has been foundthat since belts tend to stop loading at a point of saturation, there isno need to exercise great care with the liquid dispersion to assure thatthe particles are uniformly dispersed throughout. Although the particlesmay tend to load less 1 i formly than in the instance when such care isexer i if the particles are allowed to load to all areas the material toa point above the saturation, then particles above saturation may beshaken loose, resulting in uniformly loaded belt to saturation and whenused in a pow der cloud generator, such a belt will produce uniform andhigh quality pictures because of a consistent and uniform aerosol ofpowder particles output. Belts also hswc the advantage of being able toproduce fine and high quality aerosols of xerographic developer powderparticles which may be used directly for development purposes withoutother elements between the powder cloud generator and the developmentzone, such as settling chambers or the like. Another advantage of beltsload ed according to this invention is that they are compact and alsothey may be stored, producing convenient sources of powder for powdercloud generators to be called upon when needed. Loading, according tothis invention, also has the additional advantages of efiicient use ofpowder particles. That is, although only some of the powder particlesare removed from the liquid dispersion with each belt loading, none ofthe powder particles are wasted. A further advantage of belt loadingthrough immersion is the speed possible to obtain uniformly and denselyloaded belts of material. It is also noted that loading as accomplishedaccording to this invention is less cumbersome than in the instance ofloading using aerosols. When using aerosols, it is necessary to have anaerosol generator to feed particles to a loading zone, at which pointthe particles are loaded to the tape material. Such loading requiresaerosol generator, and may tie up quite a bit of other equipment, suchas compressors and the like. The ease and convenience and minimumrequirements for apparatus for loading purposes according to thisinvention result in a substantial improvement over prior-knowntechniques.

Such words as tape, belt, band, ribbon, have been used throughoutinterchangeably, and are intended to describe equivalent articles.Similar articles are also intended to be encompassed by these words.

While the present invention as to its objects and advantages, as hasbeen described herein, has been carried out in specific embodimentsthereof, it is not desired to be limited thereby, but is intended tocover the invention.

broadly within the spirit and scope of the appended claims.

What is claimed is:

l. The method of creating a uniform dispersion of fine dry developerpowder particles in gas for image development in xerography comprisingforming a liquid sus pension of xerographic developer powder particlesin a volatile nonsolvent liquid, immersing a substantially uniform tapeof porous material into the liquid suspension, removing the tape ofmaterial from the liquid suspension and drying the tape to thereby forma tape impregnated with releasable developer particles, and then feedingthe impregnated tape at a substantially uniform linear rate through asubstantially uniform gas stream producing a uniformly constant anddense dispersion of powder particles in gas.

2. The method of creating a uniform dispersion of fine dry charcoalpowder particles in gas for image development in Xcrography comprisingforming a liquid suspension of charcoal xerographic developer powderparticles in water, immersing a substantially uniform tape of nappedcotton material into the liquid suspension, removing the tape from thliquid suspension and drying to thereby form a dry tape of materialimpregnated with dry releasable developer particles, and then feedingthe impregnated tape at a substantially uniform linear rate through asubstantially uniform gas stream producing a uniformly constant anddense dispersion of dry charcoal particles in. gas.

3. The method of developing an image pattern on a xerographic platecomprising forming a liquid suspension of xero'graphic developer powderparticles in volatile nonsolvent liquid, immersing a substantiallyuniform tape of porous material into the liquid suspension, removing thetape of material from the liquid suspension and drying to thereby form adry tape impregnated with dry releasable developer particle's, feedingthe impregnated tape at a substantially uniform rate through asubstantially uniform gas stream to produce a uniformly constant anddense dispersion of dry powder particles in gas, and feed ing theparticle-in-gas dispersion to the surface of the plate to develop theimage pattern.

References Cited in the file of this patent UNITED STATES PATENTS1,803,409 Shur May 5, 1931 1,872,581 Haroldson Aug. 16, 1932 1,910,391Howard et al. May 23, 1933 1,916,333 Rose et al. July 4, 1933 2,338,480Auxier Ian. 4, 1944 2,443,782 Barnard June 22, 1948 FOREIGN PATENTS672,148 Great Britain May 14, 1952

1. THE METHOD OF CREATING A UNIFORM DISPERSION OF FINE DRY DEVLOPERPOWDER PARTICLES IN GAS FOR IMAGE DEVELOPMENT IN XEROGRAPHY COMPRISINGFORMING A LIQUID SUSPENSION OF XEOGRAPHIC DEVELOPER POWDER PARTICLES INA VOLATILE NONSOLVENT LIQUID, IMMERSING A SUBSTANTIALLY UNIFORM TAPE OFPOROUS MATERIAL INTO THE LIQUID SUSPENSION REMOVING THE TAPE OF MATERIALFROM THE LIQUID SUSPENSION AND DRYING THE TAPE TO THEREBY FORM A TAPEIMPREGNATED WITH RELEASABLE DEVELOPER PARTICLES, AND THEN FEEDING THEIMPREGNATED TAPE AT A SUBSTANTIALLY UNIFORM LINEAR RATE THROUGH ASUBSTANTIALLY UNIFORM GAS STREAM PRODUCING A UNIFORMLY CONSTANT ANDDENSE DISPERSION PARTICLES IN GAS.